You are faced with two boxes. In one you can see $1,000, but you cannot see what is in the other. You may take either box singly, or you may take both. You are told that a Supreme Being has already placed $1,000,000 in the closed box if He has predicted that you would take only the closed box. Otherwise, He has put nothing there. Furthermore this is how it has always turned out: those who have taken the one closed box have found $1,000,000, but those who took both got only $1,000. Do you take both boxes, or just the closed box? The argument for taking both is that the Supreme Being has already made his move. Whatever He has done, you get $1,000 + the contents of the closed box by choosing both, so this choice dominates any other choice (see dominance). The argument for choosing just the closed box is that the people who make this choice are the people who end up rich.

A medical Newcomb problem arises when an event that precedes some unfortunate outcome may either be a trigger, causing it, or itself be the upshot of some preceding state that causes both it and the outcome. So, for instance it may be that eating chocolate triggers migraine, or that some preceding state predisposes some people both to want to eat chocolate and to get migraines. Causal decision theory will recommend avoiding chocolate only if the chocolate is indeed a trigger; evidential decision theory will apparently recommend avoiding it even in the second case, since eating chocolate is bad news, confirming the existence of the unfortunate preceding state. See causal/evidential decision theory.